Populations of a toxic caterpillar have appeared in oak trees in west London. Spelthorne and Elmbridge.

Parents are being warned to keep children and animals away from the oak processionary moth (OPM) and their nests due to the hairs causing itching skin rashes, as well as eye and throat irritations and breathing difficulties.

The tree pest feeds on oak leaves and, in large numbers, can severely defoliate tress and leave them vulnerable to other pests and diseases.

The Forestry Commission, councils and land managers are tackling the pest with a carefully controlled programme of tree treatment and nest removal.

Ian Gambles, the Forestry Commission’s director for England, said the public could play an important role in helping to control the pest by reporting sightings.

“We need reports of the caterpillars or their nests from the public or others, such as gardeners, tree surgeons and ground-care workers, who work or relax near oak trees,” he said.

“However, they should not try to remove the caterpillars or nests themselves. This needs to be carefully timed to be effective, and is most safely done by specially trained and equipped operators.”

Affected areas include several boroughs in west and south west London, Bromley, Croydon, southern parts of Lewisham, as well as Spelthorne and Elmbridge in Surrey.

Dr Deborah Turbitt, deputy regional director for health protection, in London, endorsed the ‘don’t touch’ advice, saying: “We strongly advise people not to touch or approach the caterpillars or their nests because of the health risks posed by the hairs. Pets can also be affected, and should be kept away as well. The Forestry Commission website has pictures to help identify the pest.

“See a pharmacist for relief from milder skin or eye irritations following possible OPM contact, or consult a GP or NHS111 for more-serious reactions. Contact a vet if animals are affected. We have issued advice to local GPs and health professionals to help them identify when patients have been affected by the caterpillars and to advise them on appropriate treatment.”